In roughing the pin or journal parts of crank shafts which are generally steel, the depth of cut is large, a large dish angle is required to minimize the contact on the work-piece, and cutting edges are required to be strong as well.
Conventionally, there have been two types of inserts applied for the purpose of crank shaft machining: one is rectangular type or the other is parallelogrammic type.
A rectangular type insert has a parallelogrammic rake face to allow a large dish angle for decreasing the contact on the work-piece. In this case, error proofing in manufacturing is difficult and a positive axial rake angle is hard to be achieved.
Since a parallelogrammic type insert such as disclosed in U.S. Pat. No. 6,764,254 has a rectangular rake face, it does not provide a large dish angle. Therefore, this type of insert tends to have a large contact resistance on the work-piece of crank shafts.